The present invention relates to a thermal energy storage and delivery apparatus and a vehicular environmental control system incorporating the apparatus.
As background, the use of heating and cooling systems for vehicular applications is common and well established to maintain a comfortable environment within the vehicle while the vehicle engine is operating. When the occupants of the vehicle stop driving to rest, the interior space in the vehicle can become very uncomfortable due to the air temperature within the vehicle increasing or decreasing. In most vehicles, the heating and cooling system maintains comfort levels within the vehicle only during engine operation. These heating and cooling systems do not provide space conditioning to the interior of the vehicle when the engine is turned off.
Phase change materials ("PCMs") store heat during phase transition, typically liquid/solid phase transitions. For example, water, paraffins, alcohol, salts and salt hydrates have notably high energy densities over temperature ranges of practical significance. A large amount of thermal energy can be stored as latent heat of fusion during the melting of an appropriate PCM. The stored heat can then be extracted from the liquid PCM by cooling it until it solidifies. Thermal energy can also be stored as sensible heat in PCMs. Various attempts have been made to incorporate PCMs into heating and air conditioning systems, including heat pump systems, solar collection systems, and more conventional heating and air conditioning systems. For example, U.S. Pat. No. 5,054,540 to Carr describes a cool storage reservoir positioned in the air duct of a vehicle or the like. A plurality of elongated sealed containers are positioned in the cool storage reservoir, each of the sealed containers being filled with a gas/water medium capable of forming a gas hydrate. U.S. Pat. No. 5,277,038 to Carr also implements a thermal storage system into a vehicle using gas hydrates.
Gas hydrates, however, may possess a variety of disadvantages. Gas hydrates suffer from the development of significant pressures during decomposition and may be subject to excessive supercooling. They may also require specific devices to initiate nucleation. Another disadvantage of the U.S. Pat. No. 5,277,038 patent is that the vehicle's air distribution system is required to discharge the stored thermal energy. The vehicle air distribution system has a high power blower which drains power out of the batteries very fast. Further, the U.S. Pat. No. 5,277,038 patent discloses storing high and low temperature thermal energy of the same temperature. This does not permit the system of the U.S. Pat. No. 5,277,038 patent to provide comfortable thermal conditioning of a vehicle interior. In addition, the system disclosed in the U.S. Pat. No. 5,277,038 patent is not compatible with electric powered vehicles (EV) which don't have vehicle heating and cooling systems.
Another example is the "heat battery" designed to provide "instant" heating to a vehicle cabin. (Automotive Engineering, Vol. 100, No. 2, February, 1992). The core of the heat battery includes a series of flat, sheet metal PCM envelopes in spaced-apart relationship. The heat battery and an electric coolant pump are installed in a coolant line running from the engine to the cabin heater, forming a closed circuit capable of very rapidly heating the cabin when the engine is turned on.
U.S. Pat. No. 5,553,662 describes a thermal energy storage system operable in various heating capacity storage and discharge modes for maintaining a temperature in a vehicle compartment. Generally, the systems described in this '662 patent represent improvements over prior known systems. In the specific system disclosed, an extra pump is used in the operation of the thermal storage system, and air is circulated around the exterior of the chamber containing the thermal storage medium to recover positive or negative thermal potential. In addition, the specific thermal storage system described is not operable to condition the vehicle compartment when the engine is running, and it is not configured in a fashion which allows for discharge of the thermal storage system and simultaneous operation of the vehicle's HVAC system.
In light of this background, there remains a need for thermal storage system designs which can be operated flexibly, alone or in conjunction with conventional HVAC units, and which possess improved heat transfer properties. The present invention is addressed to these needs.